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The difficulty of obtaining on the open market accurate test charts, to record distant vision, prompted me many years ago to have these made by hand. In this manner only could one be sure that they would be mathematically correct.
They were also made in sufficient variety so as to eliminate memory in making the tests.
All of these letters, at their respective distances (200, 100, 70, 50, 40, 30, 20, 15 and 10 feet) subtend an angle of five minutes, while the component parts of the letters subtend an angle of one minute.
The B. K. Elliott Company now offers these in lithographed form.
The original letters were all made within squares divided into twenty-five squares, respectively, and the letters were drawn in such a way that the component parts of the letters include the small squares.
The sizes of the squares are as follows:
Heckel EB. CHARTS FOR TESTING EYES. JAMA. 1927;89(6):450. doi:10.1001/jama.1927.92690060001011
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